Transmissions, which have rotational speed pickup devices for generating a speed signal for a motor vehicle or the like, are known from the state of the art. These rotational speed pickup devices basically include a signal or rotational speed transmitter that is connected in a rotationally fixed manner with the corresponding transmission shaft to which a stationary rotational speed sensor is allocated in order to pick up the rotational speed at the rotational speed transmitter.
DE 198 14 758 A1 generally describes a device for recording the rotational speed of a shaft. The known device has a signal generator that is connected in a rotationally fixed manner to the shaft and configured in a manner of a toothed wheel, where the teeth of the toothed wheel each have a steep and a flat tooth flank. In addition, an analog Hall Effect sensor is provided, which picks up the rotational speed in the radial direction on the circumference of the toothed wheel, which is to say the teeth. Thanks to the varying flank gradients of the two tooth flanks, it is possible to determine the rotational speed and direction of rotation of the shaft using only one sensor and a constant update rate, even if the shaft is rotating at a very low rotational speed.
DE 103 47 494 A1 describes a similar arrangement, in which the torque on gear shafts is to be determined. For this purpose, the known device includes a gear shaft, on which a rotational speed sensing gear is arranged in a rotationally fixed manner, where the rotational speed sensing gear is, in turn, allocated with a stationary rotational speed sensor, which picks up the rotational speed in the radial direction on the circumference of the rotational speed sensing gear, which is to say on the teeth. This means that the teeth of the rotational speed sensing gear generate electric impulses upon passing the rotational speed sensor, which are fed to an appropriate evaluation unit.
A further rotational speed pickup device for a transmission of a motor vehicle is disclosed in DE 102 23 625 A1. In this rotational speed measuring device, which likewise includes a signal transmitter and a sensor, the signal transmitter is integrated in a dust protection cover for a driven shaft sealing ring. The dust protection cover is disposed outside the gearbox housing and connected in a rotationally fixed manner to the output side of the gearbox, while the sensor is attached to the outside of the housing and picks up the rotational speed in the radial direction on the circumference of the dust protection cover. The known rotational speed pickup device, however, provides no indication as to the rotational speed at which the main shaft rotates, since only the rotational speed of the output-side or output shaft is determined.
The rotational speed pickup devices, known from the state of the art, for determining the rotational speed of the main shaft of a transmission, have proven themselves, but are disadvantageous to the extent that the signal transmitter or rotational speed sensing gears increase the transmission weight, the transmission length and the transmission size. Thus there exists the possibility of picking up the rotational speed of the main shaft directly on the outer teeth of the main shaft. This would, however, once again necessitate providing long sensors or sensor holders, which are prone to vibrations and would put reliable determination of the rotational speed at risk. Furthermore, when it comes to main shafts with floating support and/or large axial play, the state of the art offers no sufficient solution. Thus it is not guaranteed in transmissions having such a main shaft that the rotational speed can be reliably picked up on the speed sensor.
The present invention is consequently based upon the objective of indicating a method for determining the rotational speed of a main shaft of a transmission which enables the simple and reliable determination of rotational speed, while overcoming the disadvantages mentioned above. In addition, the invention relates to a transmission having a rotational speed pickup device.